However, as known to a person skilled in the art, the present invention is not restricted to artificial lifting, as the valve system according to the present invention can also be utilized in other operations, for instance to inject chemicals into the well etc.
An oil and/or gas well is drilled into a hydrocarbon bearing earth formation, where the well is typically completed in order to allow hydrocarbon production from the formation. A formation like this may be comprised of several different layers, where each layer may contain one or more hydrocarbon components. Very often such a formation will also contain water, gas etc. Due to this, the conditions of production, i.e. the amount of oil, gas, water and pressure in the formation, will generally vary through the different layers of the formation, and will also be submitted to changes during the formation's time of production.
Hydrocarbon production often begins with sufficient pressure in the formation to force the hydrocarbons to the surface. As the production from the well continues, the reservoir usually loses pressure until production of hydrocarbons from the well is no longer provided by the formation pressure. Furthermore, in some wells, the formation pressure is insufficient to support the production from the well, even when the well is first completed.
Due to this, so-called artificial lift is used to supplement the formation pressure to lift the hydrocarbons from the formation to the surface of the well. The basic idea for all artificial lifting systems is to extract more hydrocarbons out of the reservoir.
For instance, an oil and/or gas well may be arranged with a sucker rod lifting system, where such a system normally comprises a drive mechanism arranged on a surface of the well, a sucker rod string and one or more downhole positive displacement pumps. Hydrocarbons can then be brought up to the surface of the wellbore, by pumping action of the downhole pump(s).
An alternative artificial lift system is a so-called gas lift system, where high pressure water or gas is injected either into the geological formation itself or into a production tubing of the well. The gas lift system may be a tubing retrievable gas lift system or a wire line retrievable gas lift system.
In the gas lift system, the high pressure gas from the surface can for instance be supplied to a space (annulus) between the production tubing and a casing of the well. The gas enters the production tubing from the annulus side, through a plurality of gas lift valves arranged along the length of the production tubing. The gas lift valves may then be positioned or arranged in the production tubing itself, or they may be arranged in so-called side pocket mandrels.
Side pocket mandrels are typically installed in a string of a production tubing in a well bore. The side pocket mandrel is provided with a full opening bore which is aligned with the bore of the production tubing and with a laterally offset side pocket bore which is designed to receive different well tools. Such well tools can be passed through the production tubing and are retrievably seated in the offset side pocket bore in order to perform or to monitor different operations in the well bore or production tubing. The well tools are retrievable and can be seated and recovered from the offset side pocket bore for instance by use of a kick over tool or similar tools. Well tools can typically include flow control devices, gas-lift devices, chemical injection devices etc., for use in conventional production operations. The side pocket mandrel may also accommodate other equipment, for instance sensors, plugs etc.
A side pocket mandrel will typically be comprised of a main mandrel body section provided with a substantially full opening main bore and a laterally offset side pocket bore, where the main mandrel body section is connected to tapered end sections by appropriate means, for instance by welding or the like. When the side pocket mandrel is connected to, for instance, a production tubing, the full opening main bore will be aligned with a bore of the production tubing, thereby allowing the production fluid to flow through the side pocket mandrel. The laterally offset side pocket bore is used to accommodate a well tool or other downhole equipment. The well tool or downhole equipment is then fastened to or seated on an inside of the laterally offset side pocket bore by means of one or more latching lugs or clamps.
The main mandrel body section is formed in such a way that the full opening main bore and the laterally offset side pocket bore are divided by an internal wall, such that well tools and/or other downhole equipment is/are separated from the production flow through the full opening bore. If the side pocket mandrel is used in a gas lift system, both the surface of the laterally offset side pocket and the internal wall of the side pocket mandrel are provided with one or more through slots or bores, such that pressurized gas introduced into the annulus can flow through the one or more slots or bores of the laterally offset side pocket and into the laterally offset side pocket bore, through a valve that is arranged inside the laterally offset side pocket bore and then into the production tubing through the slots or bores of the internal wall. The valve in the side pocket bore will then control the actual flow of the pressurized gas into the production tubing according to its specific design.
However, the pressurized gas that is released into the production tubing is normally not controlled otherwise than to break up a main injection stream of the pressurized gas into smaller streams and/or bubbles. This may result in that a significant part of the released gas stream will act against the production flow (i.e. is added with a direction downwards in the production tubing), thereby resulting in decreasing the production flow.
Furthermore, during the performing of the different operations in the well, it is often necessary to have access to the well tools and/or downhole equipment arranged in the side pocket mandrel. For instance, a gas lift valve will typically after a period of use require maintenance, repair, replacement and/or changing of the pressure setting of the gas lift valve etc. In order to carry out the necessary operation, the gas lift valve must be retrieved from the laterally offset side pocket bore. This will result in that the side pocket mandrel will be “open”, whereby a production fluid from the production tubing will be allowed to flow from the production tubing and into the annulus of the well. In order to prevent this, the well has to be shut down or closed in other ways, where this results in an undesired production standstill and increased production costs.
U.S. Pat. No. 4,239,082 “Multiple flow valves and side pocket mandrel” discloses a side pocket mandrel on a production tubing, the side pocket mandrel having two parallel inlets for gas from the surrounding annulus space to two parallel valves arranged on a common valve stem, with the two parallel valves provided each with a separate outlet to the main bore aligned with the production tubing. The valves may be gas lift valves.